Did spontaneous combustion start a backyard fire?

GWINNETT COUNTY, Ga. - Could a spontaneous combustion start a backyard fire? That may have happened at the home of a Gwinnett County couple.

Dan and Allison Kiley had a pile of mulch, pine straw and leaves sitting in their backyard when out of nowhere, they said the pile caught fire.

“It's something you hear about in school and you roll your eyes. You hear about it every so often on the news and you roll your eyes. People talk about it and you roll your eyes, not possible. Even when he’s telling me exactly what happened, I still didn't believe it,” said Dan Kiley.

Dan said that's what a fire investigator told him happened to his yard.

“The moisture from the little cold snap we had built up in the wood. You have moisture in the mulch, builds up gas almost like a sauna. Especially when we had three consecutive days over 90 and it built up and sparked itself,” said Dan.

It sent flames through their backyard. Within minutes the fence was on fire, then the trees and into the ravine.

“If this can save somebody's yard, house, neighbor’s house. It was going fast in both directions. We wanted to put it out there because this is the last thing we anticipated dealing with,” Allison Kiley.

Investigators haven't determined the exact cause, but said they cannot rule out spontaneous combustion as a potential source of ignition. Investigators said the fire did start in the wood pile, and there was no other ignition sources found at the home.